212 POLYPHASE CURRENTS. [Exp. 



simplicity in working up and comparing data relating to poly- 

 phase machinery. 



The equivalent single-phase current I' (sometimes called total 

 current) in any balanced polyphase system is the current which, 

 multiplied by the line voltage and power factor, gives the true 

 (total) power; hence 



Total power El' X power factor. 



For a 2-phase circuit, the equivalent single-phase current /' is 

 evidently twice the line current. 



For a 3-phase circuit, the equivalent single-phase current is 

 V3 times the line current. (In a delta-connection, it is seen 

 that this is three times the delta current, hence the significance 

 of total current.) 



29. Equivalent single-phase resistance R' is the resistance 

 which, multiplied by the square of the equivalent single-phase 

 current, gives the total copper loss (=RT 2 ). It will be found* 

 that for star- or mesh-connection, or any symmetrical combination 

 of star and mesh, 2-phase as well as 3-phase, R' is one half the 

 resistance measured between lines of one phase. 



For a 2-phase circuit, this becomes apparent upon inspection. 



For a 3-phase circuit, with the three equal resistances r under 

 test connected star and connected delta, determine R' and /' ; in 

 each case compare R' with r and with the resistance measured 

 between any two line-wires. 



Equivalent single-phase reactance and impedance are likewise 

 one half the measured values between lines of one phase. 



30. Current and Voltage per Phase. Current per phase and 

 voltage per phase (or phase voltage) are more commonly used 

 than equivalent single-phase quantities ; the meaning is not so 

 definite, but can generally be told from the context. The terms 



* See Standard Electrical Handbook; or Alternating Current Motors, by 

 A. S. McAllister, in which equivalent single-phase quantities are exten- 

 sively used. 



